Mesoarchean

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Aeonothem Arathem system Age
( mya )
later later later
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h
a
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Duration:

1500
Ma 		Neo-Archaic
Duration: 300 Ma 		2500
⬍
2800
Mesoarchean
Duration: 400 Ma 		2800
⬍
3200
Paleoarchean
Duration: 400 Ma 		3200
⬍
3600
Eoarchic
Duration: 400 Ma 		3600
⬍
4000
formerly: Hadaikum

The Mesoarchean is a geological era . It represents the third of four eras within the geological eon of the Archean (Mesoarchean = "middle Archean"). It begins about 3200 million years ago BP with the end of the Paleoarchean and ends about 2800 million years ago BP with the beginning of the Neoarchean . Its duration is 400 million years.

Redefinition of the Mesoarchean

In the course of moving away from period boundaries determined purely by radiometry, the GSSP principle should now be applied as far as possible in the Precambrian, according to Gradstein et al. (2012) . Periods are now defined in terms of significant geological events rather than arbitrary radiometric ages.

Since the Eoarchaic no longer applies, according to Gradstein, the Mesoarchaic begins much earlier, namely at the GSSP of the Vaalbarum , which is set at 3490 million years BP. This GSSP comes to lie at the lower edge of the Dresser Formation belonging to the West Australian Warrawoona Group , which concordantly overlays the pillow basalts of the North Star Basalt . The Vaalbarum follows as the second period of the Mesoarchean at 3020 million years BP, the Pongolum , which is also defined by a GSSP (concordant contact between the basal conglomerate and the quartz-rich sandstone above it of the Gorge Creek Group ( De Gray Supergroup ) in Western Australia) . The Pongolum lasts until 2780 million years BP and is separated by a GSSP from the subsequent Neo-Archean or its first period, the Methanium . The GSSP, which concludes the Mesoarchean, is being relocated to the base of Mount Roe Basalt in Western Australia. The Mount Roe Basalt belongs to the Fortescue Group and thus to the Mount Bruce Supergroup . The newly defined Mesoarchean lasts a total of 710 million years.

meaning

Stromatolites of the approximately 3,400 million year old Strelley Pool Formation of the West Australian Pilbara Craton

The main characteristic of the Mesoarchean is undoubtedly the first appearance of macroscopically recognizable life . The oldest known stromatolites appear at the base of the Dresser Formation . After the meteorite bombardment has finally subsided, their spread is linked to the emergence of the first stable continents (or continent germs) and their floating lithospheric roots. The stromatolites in the Mkhonjwa Mountains northeast of Barberton in South Africa and in Steep Rock Lake, NW Ontario in Canada, in which fossils of cyanobacteria were found, date back to 3200 and 2800 million years ago BP.

With the Pongolum, terrestrial sedimentary basins appear for the first time , which were able to form on stabilized continents . In powerful, undisturbed sequences on shelf platforms , the colonization of flat, sandy areas of the facies by microbes can be demonstrated.

Icing

The Pongola glaciation occurred about 2,900 million years ago. It can be verified by two diamictite horizons in the Mozaan Group of the Pongola Supergroup ( Delfkom formation ).

Meteorite impacts

In the period 3470 to 3240 million years BP, four horizons were deposited within the Swaziland Supergroup of the South African Kaapvaal Kraton , which indicate possible meteorite impacts . The lowest horizon can also be found in the Warrawoona Group of the West Australian Pilbara Kraton .

stratigraphy

Significant geological formations

Deposits

Magmatism

Geodynamics

Orogenesis

See also: Geological timescale

Individual evidence

  1. ↑ Geology as a place of learning. ( Memento of the original from July 14, 2010 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF; 4.4 MB, p. 2) on the website of the Bavarian State Ministry for Environment and Health , www.stmug.bayern.de @1@ 2Template: Webachiv / IABot / www.stmug.bayern.de
  2. ↑ Thomas R. Becker: The measurement of earth time - a historical-methodological overview in: Ewige Moments: An interdisciplinary approach to the phenomenon of time. Ed .: Veronika Jüttemann, Waxmann Verlag, ISBN 978-3-8309-2011-3 , p. 57 books.google.de
  3. ^ Felix M. Gradstein et al .: On the Geologic Time Scale . In: Newsletters on Stratigraphy . tape 45/2 , 2012, p. 171-188 .
  4. ^ Stromatolites in the early days of the earth's history. ( Memento from July 31, 2012 in the web archive archive.today ) In: Faculty of Geosciences and Geography at the University of Göttingen
  5. ↑ Robert E. Kopp, Joseph L. Kirschvink, Isaac A. Hilburn, Cody Z. Nash: The Paleoproterozoic snowball Earth: A climate disaster triggered by the evolution of oxygenic photosynthesis . In: Proceedings of the National Academy of Sciences . tape 102 , no. 32 , August 9, 2005, ISSN  0027-8424 , p. 11131–11136 , doi : 10.1073 / pnas.0504878102 , PMC 1183582 (free full text).
  6. ↑ Roland Walter: Earth history: the formation of the continents and oceans. de Gruyter, Berlin 2003, ISBN 978-3-11-017697-1 , p. 51 books.google.de
  7. ↑ Lowe, DR et al .: Spherule beds 3.47 - 3.24 billion years old in the Barberton Greenstone Belt, South Africa: A record of large meteorite impacts and their influence on early crustal and biological evolution . In: Astrobiology . v. 3, 2003, p. 7-47 .
  8. ^ DR Lowe, GR Byerly: Stratigraphy of the west-central part of the Barberton Greenstone Belt, South Africa . In: DR Lowe, GR Byerly (Ed.): Geologic evolution of the Barberton Greenstone Belt, South Africa. Geological Society of America Special Paper . tape 329 , 1999, pp. 1-36 .
  9. ^ Axel Hofmann: The geochemistry of sedimentary rocks from the Fig Tree Group, Barberton greenstone belt. Implications for tectonic, hydrothermal and surface processes during mid-Archaean times . In: Precambrian Research . tape 143 , no. 1-4 , December 15, 2005, pp. 23-49 , doi : 10.1016 / j.precamres.2005.09.005 .
  10. ^ SL Kamo, SW Davis: Reassessment of Archean crustal development in the Barberton Mountain Land, South Africa, based on U-Pb dating . In: Tectonics . tape 13 , 1994, pp. 167-192 .
  11. ^ JW Goodge, CM Fanning: 2.5 billion years of punctuated Earth history as recorded in a single rock . In: Geology . tape 27 , 1999, p. 1007-1010 .
  12. ↑ JW Goodge, among others: U-PB evidence of 1.7 Ga crustal tectonism during the Nimrod Orogeny in the Transantarctic Mountains, Antarctica: implications for Proterozoic plate reconstructions . In: Precambrian Research . tape 112 , 2001, p. 261-288 .
  13. ^ MJ Robertson, among others: Gold mineralization during progressive deformation at the Main Reef Complex, Sheba Gold Mine, Barberton Greenstone Belt, South Africa . In: Africa. Econ. Geol. Res. Unit Inf. Circ. tape 267 . University of Witwatersrand, 1993, p. 1-26 .
  14. ^ G. Chi, inter alia: Formation of the Campbell-red Lake gold deposit by H 2 O-poor, CO 2 -dominated fluids . In: Mineralium deposita . tape 40 , 2006, pp. 726-741 .
  15. ^ SA De Waal: Nickel minerals from Barberton, South Africa. VII. The spinels Co-chromite and Ni-chromite and their significance for the origin of the Bon Accord nickel deposit . In: Bull.BRGM II (2), 1978, p. 223-230 .